                Patent Literature 1: JP 2012-98863 A        Patent Literature 2: JP 2006-72672 A        Patent Literature 1 discloses a technique of distinguishing whether a palette has passed on a conveyor or near the conveyor. The technique disclosed in Patent Literature 1 includes placing a reader-writer near the conveyor as well as disposing a fixed tag to face the reader-writer with the conveyor interposed therebetween. The palette moving on the conveyor also has a tag (hereinafter, a moving tag) affixed thereto.        
When the moving tag is affixed to the palette moving on the conveyor, the moving tag is occasionally positioned between the fixed tag and the reader-writer facing each other with the conveyor interposed therebetween. The moving tag positioned between the fixed tag and the reader-writer inhibits communication between the fixed tag and the reader-writer. The moving tag is closer to the reader-writer than the fixed tag in this state and thus achieves excellent communication with the reader-writer.
The palette then moves on the conveyor and the moving tag affixed to the palette becomes no longer positioned between the fixed tag and the reader-writer, so that the fixed tag and the reader-writer achieve excellent communication. Meanwhile, the moving tag and the reader-writer become incommunicable.
The moving tag Is determined as being affixed to an object moving on the conveyor when such change is observed.
In contrast, the object having the moving tag affixed thereto and passing near the conveyor never inhibits communication between the fixed tag and the reader-writer. It is thus possible to distinguish whether the palette having the moving tag affixed thereto is passing on the conveyor or near the conveyor.
Patent Literature 2 discloses placing a fixed tag at each gate. The fixed tags are each positioned so as to be incommunicable from the other gates. The gates are each provided with a reader configured to communicate with the corresponding fixed tag. A moving tag is determined as being passing the gate when the corresponding reader is communicable with the moving tag and is incommunicable with the fixed tag.